Like finding a needle in a haystack of uncertainty, Peter Berg manages to pinpoint the moment Wayne Gretzky was confident about being traded to the Los Angeles Kings.

It was the summer of 1988, and Kings owner Bruce McNall received an unexpected phone call.

One day Wayne was in my office and (Edmonton Oilers owner Peter Pocklington) called, and I didn't know it was Peter, so I hit the speaker, and ... right away Peter starts on me about the trade with Wayne. ‘Wayne is not good for Edmonton anyway.' He was trying to justify in his own mind that it was OK to trade Gretzky. ‘He's got this girlfriend now, an actress, and he's complaining all the time, it's a problem, and I'm just as happy to do something like this.' When Wayne heard this, it just flipped everything. Then from that moment on, when we hung up, Wayne said ‘I'm an L.A. King.'

This is the turning point as revealed in Berg's film "Kings Ransom," a documentary of the Gretzky trade which airs at 8 p.m. tonight on ESPN2. The director manages to gather all the principals involved in the deal – Gretzky, McNall and Pocklington, to name a few – to reminisce and provide narration for the events preceding and following August 9, 1988.

In an exclusive interview with HockeyPrimeTime.com, Berg said that each was forthcoming, but still conflicted about the trade 21 years later.

"Depending on what day you catch them, they'd tell you they regret it happened, or tell you they're glad it happened," he said. "(Gretzky) regrets he was traded at times; he understands he was traded at times."

Berg was one of 30 filmmakers invited by ESPN to direct a film for the network's "30 for 30" series, and each was given creative license to choose his topic. Berg was living in Los Angeles at the time of the trade and considers himself a "big hockey fan," making the Gretzky trade a logical choice.

"It was a very memorable part of my L.A. experience," he said. "As soon as I heard about the trade, I bought season tickets."

In his first documentary, Berg puts the kind of heavy touch on the film that one would expect from his background ("Hancock," "Friday Night Lights"). Hockey highlights from the 1980s are set to dooming background music; storm clouds roll over the Edmonton skyline as August 9 approaches; clips of the motorcade carrying Gretzky in a Stanley Cup victory parade seem to anticipate an assassination attempt.

But the director manages to put the dramatic effect into perspective: There's no comparing this to any other trade in any other sport, he points out to Greztky while the two play a round of golf in the film.

As Gretzky tees off, Berg asks, "how many (championships) could you have won if you stayed in Edmonton?"

"The team was good enough, I don't know, I could have won four more," said Gretzky, a number Berg finds low.

For all the lessons the documentary offers the past, there's a greater message for the future of hockey, Berg believes.

"These guys weren't centering themselves, thinking about their marketability like in other sports," he said. "I think it kind of hurts hockey."